Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an activated carbon adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
Adsorption of fuel vapor to activated carbon is an exothermic reaction. A hot canister thus has a lower adsorption capacity than does a cool canister. In hot climates, and/or following a prolonged driving period, the canister temperature may become increased due to heat rejection from the engine, exhaust, asphalt radiation, etc. As such, the canister may be incapable of storing enough fuel vapor to accommodate an tank filling refueling event without emitting hydrocarbons into atmosphere.
Other attempts to address hydrocarbon breakthrough during refueling events include deposing a secondary or “trap” canister downstream of the primary fuel vapor canister in order to capture breakthrough hydrocarbons. One example approach is shown by Mani et al. in U.S. Pat. No. 9,005,352. Therein, a trap canister with a higher adsorbance than the main canister is selectively coupled to an outlet of the main canister within the fuel canister vent pathway.
However, the inventors herein have recognized potential issues with such systems. As one example, a trap canister must significantly restrict vapor flow in order to be effective. This may lead to prolonged fuel tank depressurization and may further limit the rate of refueling and the rate of purging the canisters. If the trap canister is bypassed, hydrocarbon breakthrough may occur.
In one example, the issues described above may be addressed by a method, comprising: during a first condition, including an active refueling event, receiving an indication of hydrocarbon breakthrough from the fuel vapor canister; and restricting flow of fuel vapor through a fuel vapor canister vent pathway responsive to the indication of hydrocarbon breakthrough. Restricting the fuel vapor canister vent pathway will cause fuel tank pressure to increase, thus triggering an automatic shutoff of a refueling dispenser. In this way, the refueling event may be terminated without releasing significant quantities of hydrocarbons into the atmosphere.
As one example, a hydrocarbon sensor may be placed in the canister vent pathway to detect hydrocarbon breakthrough, and a canister vent valve may be actuated to a closed conformation to restrict vapor flow. By restricting refueling in this way, vehicles can obtain fuel without increasing surface hydrocarbon concentrations which may thus limit ground ozone levels on hot days.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.